Jack McCoy has a habit of playing fast and loose with the rules. He also isn’t very fond of disclosure. Back when old Jack was Executive ADA his assistants often had to convince him to disclose favorable evidence to the defense. The lovely ladies weren’t soft-hearted; they were being pragmatic—and practicing safe law and following the Brady Rule (named for Brady v. Maryland), requires prosecutors to disclose materially exculpatory evidence in the government’s possession to the defense.
According to the model rules of professional conduct (and a little old ruling by the Supreme Court), “a prosecutor in a criminal case is duty-bound to make timely disclosure to the defense of all evidence known to the prosecutor that supports innocence or mitigates the offense.” In other words, if Jack has evidence that supports Jill’s contention of innocence, he is required by law to hand it over to her defense attorney.